Myocardial revascularization is a technique, known in the art, for creating channels in ischemic heart tissue to improve the blood supply to ischemic myocardium. It may be performed by various techniques, the best-known of which is laser myocardial revascularization, which employs laser radiation for generating such channels.
In transmyocardial revascularization (TMR), as is known in the art, a computer-controlled laser is used to drill penetrating holes about 1 mm in diameter in the myocardium by delivering laser energy to the epicardium through an incision in the chest and the pericardium. Blood at the outer, epicardial openings of the channels typically clots after a few minutes, but the inner portions of the channels, communicating with the ventricle, remain patent. It is hypothesized that during systole, blood flows through these channels into naturally-existing myocardial sinusoids, supplementing the impaired arterial blood supply.
According to another hypothesis, the local injury caused to the myocardium by various forms of energy (e.g., laser radiation, as described above, or alternatively, RF radiation, or ultrasonic or mechanical energy) stimulates local angiogenesis, eventually supplementing the impaired arterial blood supply. Although there are no conclusive answers at present regarding the underlying mechanism, there is clinical evidence of the treatment's therapeutic efficacy.
U.S. Pat. No. 5,389,096, to Aita, et at., which is incorporated herein by reference, describes methods and apparatus for percutaneous myocardial revascularization (PMR). A deflectable, elongated lasing apparatus is guided to an area within the patient's heart, and the distal end of the apparatus is directed to an area of interest in the inner wall of the heart. The wall is irradiated with laser energy to form channels therein, preferably without perforating the epicardium. Alternatively, PMFR may be carried out by applying other energy forms, as described above, from inside the art.
In TMR, as is known in the art, the channels are created through the myocardium from the outside in, and the transient blood stream ensuing upon channel completion constitutes an intrinsic indication of successful drilling. In PMR, however, the channel is generated from inside the heart chamber and, preferably, does not penetrate the myocardium. Consequently there is no direct indication of successful generation of the channel.
A PMR procedure, whether employing laser energy or any other suitable energy form, may fail due to a multiplicity of reasons. For example, referring specifically to laser PMR, the catheter inserted into the heart may be incorrectly oriented, so that the energy does not impact and penetrate the endocardium, or does not penetrate to a significant depth. Alternatively, the distal end of the catheter may be obstructed, for example, by a thrombus and/or ablated tissue residues. Because systems for PNR known in the art do not give any indication of whether the energy pulse has successfully generated a channel in the myocardium, it is difficult or impossible for an interventional cardiologist to detect and correct such a failure during the procedure.